Electrodeposition of molybdenum



United States Patent ELEC'IRODEPOSI'IION OF MOLYBDENUM ChristianJ. Wernlund, Niagara Falls, N.Y., assignor to E. I. du Pont de Nemours'and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Filed Feb. 11, 1958, Ser. No. 714,492

8 Claims. (Cl. 20414) This invention relates to the electrodeposition of molybdenum to form electroplated. coatings. on ferrous and other metal surfaces.

Although large tonnages of molybdenum powder are. made by the reduction of mol'ybdenumoxides With hydrogen at around 1200 C. the electrolytic reduction from either aqueous or organic. electrolytes has thus far not been effected so far as known. Electrophoretic deposition ofmolybdenum particles aloneor mixed with molybdenum oxide particles on metal or ceramic surfaces has been reported. High voltages and subsequent treat ment at about 1200 C. with hydrogen is required. Sintering and compression of the porous molybdenum under 50,000 to 100,000.-p.s;i. is finally necessary. A coating so produced is obviously very expensive and not applicableto low melting metals. I Molybdenum coatings on metal surfaces such as, iron iron alloys, copper, aluminum and the like arehighly desirable because of the resistance of molybdenum to corrosion, erosion and high temperatures. The molybdenum deposit also has the useful property of being ductile.

It is therefore an object of the present invention to provide a process for the electrodeposition of molybdenum. It is a further object to provide electrolytes suitable for the electrodeposition of molybdenum.

I have now discovered that smooth, bright, uniform deposits of molybdenum are produced by the use of glycerine baths containing not over about 15 by weight of Water. The baths contain up to about 10% anhydrous alkali hydroxide and up to 10% molybdennum anhydride. The solution formed resembles an aqueous solution, conducts the electric current and can be used to plate molybdenum metal on other clean metal surfaces. My invention is further illustrated but not limited by the following examples.

Example 1 A solution comprising 83 g. anhydrous glycerine of reagent grade, one g. sodium hydroxide and g. of molybdenum anhydride was prepared at 132 C. by stirring the components in a steel crucible of 2 /2 in. diameter and 2 in. deep. A sheet nickel anode having an immersed area of 0.75 sq. in. was introduced into the bath together with a polished sheet copper cathode having an equal submerged area as the anode. The cathode and anode were about one inch apart. The solution was electrolyzed for 140 minutes at volts and 0.3 amp. at 120 C. and at 0.9 amp. at 132 C. It is assumed that some of the hexavalent molybdenum was reduced to a lower valence. A clean copper wire having a submerged area of 0.2 sq. in. was now used as the cathode and on electrolysis at 107 C. for 10 minutes, volts and 0.10 to 0.12 amp. a bluish bright molybdenum deposit weighing 0.0025 g. (equivalent to 1.8 g. molybdenum/sq. ft.) was secured.

Example 2 The solution and crucible from the Example 1 was used. A nickel anode and a clean copper wire cathode 7 2,943,029 Patented June 28, 1960.

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Example 3 A solution comprising 160 g. anhydrous glycerine, 8.8 g. sodium hydroxide and 8.8 g. molybdic anhydride was. prepared by stirring the mixture at 130 C. in a 250 ml. Pyrex beaker. Electrolysis was conducted with a cooper cathode having a submerged area of 3 sq. in. for 250 min. The current varied from 1.0 to 2.4 amps. at 11.0 to 20 volts at to 135 C. The cathode was now replaced by a clean, polished, weighed copper cathode and plated over an area of 0.75 sq. in. at 0.9 to 1.6 amps. at 20. volts for 15 minutes at a temperature around about. 136 C. A bright molybd'enumdeposite weighing; 0.0034 g. was secured.

Example 4 In 130 gof anhydrous glycerine contained in a 250 ml. pyrex beaker 8 g. of sodium hydroxide was first dissolved at 125 C. and then 8 g. of molybdic anhydrid'ewas added and solution completed. The solution was subjected to electrolysis for 18 minutes at 20 volts and 1.5 to 1.8 amps. at 125133 C. At this point the electrolyte was cooled to 90 C. and 5 g. water added. A weighed, polished copper cathode having an exposed area of 0.75 sq. in. was-subjected to electrodepositingin thisbath at- 20 volts; 2.2-2.7 amps at 112-l-40 C. for 10 minutes. A pleasing bright molybdenum deposit weighing 0.0058 g. (equivalent to 1.11 g. molybdenum-k sq. ft.) was secured.

Example 5 To 80 g. of glycerine there was added 7 g. of sodium hydroxide, 12 g. of molybdic anhydride and 10 g. water. Two sheet nicikel anodes having a combined submerged area of 2 sq. in. together with 'a copper cathode having 0.6 sq. in submerged area were used in electrolysis of this bath for minutes to condition the electrolyte. A Weighed, polished copper cathode having a submerged area of 0.62 sq. in. was now electroplated for 11 minutes at 112 C. to 117 C. at 20 volts and 0.70 to 0.78 amp. A bright bluish molybdenum deposit weighing 0.0025 g. (equivalent to 0.58 g. molybdenum/sg. ft.) was secured.

In general, I have found it requisite to condition a newly prepared glycerine bath containing molybdenum oxide and alkali metal hydroxide by conducting a reducing electrolysis therein before attempting to plate molybden-um therefrom. It is not known precisely why such preconditioning is advantageous but, without restricting myself in this respect, it may be that a lower valent molybdenum compound is produced by the preelectrolysis of the electrolyte. The bath can, of course, be used directly for the electrodeposition of molybdenum from the freshly prepared bath but in that case it will take a longer time to deposit a suitable layer of molybdenum. After a bath has once become conditioned it may be used indefinitely, provided addition of molybdenum and other components is made as they are lost from the bath.

Anhydrous glycerine is preferred as the solvent component for plating molybdenum but some water may be present. In general, the water present should not be much in excess of about 15% by weight of the glycerine since the utility of the electrolyte seems to decrease rapidly with larger amounts of water.

In general, it is preferred to have present in .the electrolyre as much alkali metal hydroxide as will dissolve therein. The range of suitable concentration will 'be between 1.0% and up .to 10 to 15% depending upon the solubility in the glycerine at the temperature used.

The metal hydroxide must be present in the electrolyte to solubilize the molybdenum oxide. Sodium hydroxide is preferred, but potassium and the other alkali metal hydroxides can also be used.

The molybdenum of the electrolyte is suitably added as molybdic oxide anhydride (M There should be present in the bath at least 0.5% by weight of the glycerine of molybdenum oxide and the concentration of the oxide may be as high as the degree of solubility in the caustic-glyceriue electrolyte bath will permit. The preferred concentration of molybdenum oxide will be between about 1% and 12% by weight of the glycerine.

' In general, the weight of the molybdenum oxide present will equal the weight of the alkali metal hydroxide.

Electrodeposition of molybdenum from my solutions may be accomplished at temperatures between about 90 and 150 C. In general, the higher temperatures, between about 120 to 150 C. are preferred.

Electrodeposition in general will require a voltage, be: tween about and 20 volts, depending in part on. the temperature of the bath, the concentration of electrolytes therein and-the distance between the electrodes, but the invention is not limited in this respect.

I claim:

1. The process of electrodepositing molybdenum comprising the electrolysis with a metal cathode of a bath consisting essentially of glycerine, alkali met:.l hydroxide and molybdenum oxide, said hydroxide and oxide each comprising between about 1% and 12% by weight of the glycerine.

2. The process of electrodepositing molybdenum comprising the electrolysis with a metal cathode of a bath consisting essentially of glycerine, sodium hydroxide, and molybdenum oxide, said hydroxide and oxide each comprising between about 1% and 12% by weight of the y l e 3. The process of electroplating molybdenum comprising the electrolysis with a metal cathode of a bath consisting essentially of glycerine, water not to exceed 15% by weight of the glycerine, sodium hydroxide and molybdenum oxide, said hydroxide and oxide each comprising between about 1% and 12% by weight of the glycerine.

4. The electroplating composition consisting essentially of glycerine, water not to exceed 15 by weight of the glycerine. and between about 1% and 12% by weight of the glycerine of each of molybdenum oxide and of sodium hydroxide.

5. A process for the electrodeposition of molybdenum on a base metal comprising passing a current between an anode and said basemetal as cathode in a bath consisting essentially of a glycerine solution of an alkalimetal hydroxide and at least 0.5% by weight of molybdenum oxide based on said glycerine.

References Cited in the file of this patent UNITED STATES PATENTS Yntema et al. Mar. 7, 1950 OTHER REFERENCES I Wolf: Chemical Abstracts, vol. 13 (1919), pp. 2644- 2645.

, Reid et al.: Journal Electrochemical Society, vol. 104 (January 1957), pp. Ll-22. 

1. THE PROCESS OF ELECTRODEPOSITING MOLYBDENUM COMPRISING THE ELECTROLYSIS WITH A METAL CATHODE OF A BATH CONSISTING ESSENTIALLY OF GLYCERINE, ALKALI METAL HYDROXIDE AND MOLYBDENUM OXIDE, SAID HYDROXIDE AND OXIDE EACH COMPRISING BETWEEN ABOUT 1% AND 12% BY WEIGHT OF THE GLYCERINE. 